Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$226.33	12.701%	$255.0762	$255.08	$255.10	$255.10
Purchase #2	$249.73	12.496%	$280.9363	$280.94	$280.95	$280.90
Purchase #3	$223.36	12.143%	$250.4826	$250.48	$250.50	$250.50
Purchase #4	$13.32	8.288%	$14.424	$14.42	$14.40	$14.40
Purchase #5	$30.30	5.104%	$31.8465	$31.85	$31.85	$31.80
Purchase #6	$60.77	11.692%	$67.8752	$67.88	$67.90	$67.90
Purchase #7	$103.75	13.347%	$117.5975	$117.60	$117.60	$117.60
7 purchase totals =	$907.56		$1,018.2383	$1,018.25	$1,018.30	$1,018.20